Progressive Multifocal Leukoencephalopathy (PML) is a fatal demyelinating disease of the brain and is caused by lytic infection of oligodendrocytes, the myelin-producing cells of the CNS, with the human neurotropic polyomavirus, JC virus (JCV). JCV infects most people in childhood and then remains in a persistent but dormant state known as latency where the level of JCV replication remains low. However, in the context of severe immunosuppression, especially AIDS, JCV becomes reactivated in the brain where its replication leads to PML. The mechanisms involved in the reactivation of JCV in the brain and the initiation of PML are unknown but are thought to involve effects of immunosuppression on cytokines such as TNF-1, or direct effects of HIV-1 via its transactivator, Tat. Our preliminary data point to the involvement of a specific site (kB) within the control region that binds NF-kB to stimulate transcription and hence replication of the JCV genome. This site also binds C/EBP2 isoforms to inhibit transcription. Our hypothesis is that the balance of JCV latency and reactivation to PML is regulated by the NF-:B and C/EBP2 transcription factors, which are both regulated by cytokines whose levels are dysregulated during the course of HIV-1 infection. We propose a comprehensive experimental analysis of the roles of these cytokines and transcription factors in determining the balance of JCV latency and reactivation to initiate PML. The role of cytokine stimulation, NF-kB and C/EBP2 on JCV transcription, replication and life cycle will be analyzed. Mutant forms of the kB promoter element and C/EBP2 mutants will be analyzed to investigate the molecular mechanisms involved. We will also investigate the effect of HIV-1 Tat, since Tat is a potent transactivator of JCV that can activate NF-kB signaling and also binds to C/EBP2. The pathological importance of these findings will be assessed using PML clinical samples and controls. Through these studies, we hope to gain a better understanding of the molecular mechanisms involved in JCV latency and reactivation to cause PML and this may open new therapeutic avenues to this disease. PUBLIC HEALTH RELEVANCE Progressive Multifocal Leukoencephalopathy is a fatal degenerative brain disease that is caused by a virus called JCV that runs out of control when the immune system is damaged. This disease afflicts about 5% of people with HIV/AIDS. The aim of this proposal is to find out what makes the virus grow in these patients so that we can develop treatments.